The present invention relates to cuvettes and methods for using cuvettes. Oximetry modules are common components of medical-diagnostic analyzer systems and in particular of blood gas analyzers. Such blood gas analyzers are for example developed as portable analyzers for determining POC (point of care) parameters, for example the blood gases (O2, CO2, pH), the electrolytes (e.g., K+, Na+, Ca++, Cl−), the metabolites (e.g., glucose and lactate), the haematocrit, the haemoglobin parameters (e.g., tHb, SO2, etc.), and bilirubin and are primarily used for the decentralized determination of the above-mentioned parameters in whole blood samples.
Ideally it should also be possible for “untrained” users to simply and intuitively operate such analyzers. Another important requirement for such an instrument is that it should be possible to operate it “virtually maintenance free” from the point of view of a user. “Virtually maintenance free” is generally understood to mean that also a (technically) untrained user only has to exchange consumables that are present in the form of cassettes and/or modules for the routine operation. It should be possible for the user to exchange all consumables by simple intuitive handling steps.
In systems such as those described in U.S. Pat. No. 3,972,614 the optical measuring chamber (cuvette) is designed as an integral component of the oximeter which remains permanently in the instrument. The analyzer described in U.S. Pat. No. 3,972,614 for the spectroscopic determination of parameters in blood samples such as, e.g., haemoglobin, also comprises means for the ultrasonic haemolysis of the blood sample, i.e., the destruction of the red blood corpuscles, in order to make the blood sample as free of scattering bodies as possible. Only by this means is it then possible to spectroscopically analyze the sample.
However, a disadvantage of the known system is the high risk of blockage during the planned period of use where in particular the fluidic coupling sites and the small pathlength of the sample channel are problematic. If dirtying or blockages occur in the cuvette area of these oximeter systems, they can often only be eliminated by a complicated exchange of the cuvette. This usually requires an appropriate training or a service technician has to be called thus frequently resulting in long unscheduled downtimes of the analyzer. Furthermore, the manual replacement of a cuvette in such systems often requires subsequent manual adjustment and calibration steps in order to again obtain reproducible measuring results.
A method and an instrument for the spectroscopic measurement of analytes in samples is known from the document EP 1586 888 A2. The instrument comprises a light source which generates a light path, a photodetector at the end of the light path and a slit opening in the light path into which a cuvette filled with the sample can be manually inserted. The cuvette is a simple plastic part which consists of a well provided with a handle for holding the sample and a cover which is joined to the well in a hinged fashion. This cuvette is a simple disposable product which is not suitable for carrying out a haemolysis and is also not intended to be used for this purpose. Rather it is described that the instrument is to be used for spectroscopic haemoglobin measurements as an indicator for haemolysis that has occurred in the sample. Another intended use of the known instrument is to monitor the decomposition or the reversal of decomposition of haemoglobin-based blood substituents by measuring methaemoglobin. Due to its simple construction, the known cuvette is not dimensionally stable when pressure is applied and can therefore in no way be used in analytical systems in which it is mechanically pretensioned and/or stressed as is for example necessary for ultrasonic haemolysis. The lack of dimensional stability has a major effect on the result of spectroscopic measurements. Hence an accurate spectroscopic analysis of blood samples is not possible with this cuvette.
Therefore there is still a need for a cuvette which can be arranged in an exchangeable manner in a spectroscopic analyzer and is suitable for accurate analyses.